What is the ruling regarding a wife who lied to her husband after he told her: "If you lie to me, you are unlawful to me," knowing that if she had not lied, "her home would have been destroyed"?

What the husband did was to suspend the prohibition of his wife upon her lying. If she lied to him, the prohibition takes effect, and the fact that the lie was out of necessity does not prevent its occurrence. The preponderant opinion is that the prohibition of the wife refers back to the husband's intention. Therefore, the husband must be informed to ascertain his intention, and the wife can ask for his pardon, explaining that her intention was good.